1. Field of the Invention
Apparatuses consistent with the present invention relate to a rear projection display, and more particularly, to a compact, small, thin rear projection display for use in mobile devices.
2. Description of the Related Art
Generally, mobile devices such as laptop computers, personal digital assistants (PDAs), and cell phones use liquid crystal displays (LCDs) or organic light-emitting devices (OLEDs), which are thin and light and have low power consumption. However, display devices, such as LCDs or OLEDs, include a rim portion around an image displaying area, where an image is not displayed, where driving circuitry is mounted. For example, cell phones or laptop computers include a display in a cover unit which is connected to a main body unit in which a main board and a keypad are installed. The image displaying area is only 60 to 80% of the entire area of the cover unit. Thus, it is difficult to increase the size of the display.
Accordingly, a technique of utilizing almost the entire surface of the cover unit as an image displaying area by employing front or rear projection displays in mobile devices, such as, laptop computers, PDAs, or cell phones, has been under development. Furthermore, in view of recent mobile multimedia broadcasting services like digital multimedia broadcasting (DMB), the displays of small mobile devices like cell phones should be enlarged as much as possible.
FIGS. 1 through 3B illustrate conventional rear projection displays that can be used in such mobile devices. FIG. 1 illustrates a projection display for computers disclosed in U.S. Pat. No. 6,525,750. Referring to FIG. 1, in the conventional rear projection display, an image signal generated in a main body 10 is transmitted to a projector 11 placed in an upper portion of a screen 15 through a cable 12. The projector 11 generates an image according to the image signal and projects the image on a magnifying mirror 14. Then the image is magnified by the magnifying mirror 14 and projected onto the screen 15. When not used, the magnifying mirror 14 can be retracted into the main body 10 by a tray 13.
FIG. 2 illustrates a “compact projection system” disclosed in U.S. Pat. No. 6,637,896. Referring to FIG. 2, a projector 21 is installed at a side of a main body 20, such as a cell phone, by a retractable connecting member 22. Furthermore, a foldable screen 23 is installed in an upper portion of the main body 20. An image signal generated in the main body 20 is transmitted to a projector 21 via the retractable connecting member 22, and the projector 21 projects an image to the foldable screen 23. When not used, the foldable screen 23 can be folded over a top surface 24 of the main body 20.
FIGS. 3A and 3B illustrate a “flat panel display” disclosed in U.S. Pat. No. 6,870,671. Referring to FIG. 3A, an image projected by a projector 31 is incident on a side of a transparent plate 33 through a mirror 32 and travels inside the transparent plate 33 by total internal reflection. Then, the image is incident on a side of a tapered glass 36 through a cylindrical lens 34. Mirrors 35a and 35b are attached to top and bottom surfaces of the cylindrical lens 34 to prevent the image from being emitted to the outside. As illustrated in FIG. 3B, since the glass 36 is tapered, a portion of the image traveling within the glass 36 does not satisfy the total internal reflection condition. Thus, the portion of the image which is not under the total internal reflection condition is emitted to the top surface of the glass 36. Accordingly, the image can be observed through a screen 37 formed on the top surface of the tapered glass 36.
However, during assembly of each of the above-described conventional small-sized rear projection displays, it is difficult to accurately arrange the components thereof. Also, the conventional projection displays illustrated in FIGS. 1 and 2 may easily break down because the mirror 14 and the projector 21 are retractable. Moreover, in order to display an image accurately, the mirror 14 and the projector 21 should be fixed at accurate positions, and the screens 15 and 23 facing the mirror 14 and the projector 21, respectively, should be erected at exact angles. In the conventional projection display illustrated in FIG. 3, a coating layer having a complex structure should be formed on a tapered surface of the glass 36 so that an image can be emitted from an accurate location on the tapered surface.